Heat sealable carton structure and method of making



June 21, 1966 D. B. BOWMAN ETAL 3,257,055

HEAT SEALABLE CARTON STRUCTURE AND METHOD OF MAKING Filed Oct. 6, 1958 United States Patent O Claims priority, application Great Britain, Oct. 15, 1957,

32,252/57 '8 Claims. (Cl. 229-31) This invention relates to cartons and in particular to cartons such as are Aused to contain goods which in storage or transit are liable to lose moisture or to gain moisture. Examples of such goods are frozen goods which tend to lose moisture in refrigerating conditions, and confectionery and cereals which tend to gain moisture from the atmosphere.

To protect goods against these conditions it has been proposed to enclose them in cartons formed from glosswaxed blanks, that is blanks coated with a low viscosity paraffin wax. However, the known forms of gloss-waxed cartons cannot be effectively sealed either by adhesive or by heat sealing because the wax employed is of such a nature that it can be applied mechanically only to the whole surface of the blank and it is not possible so to gloss-wax a blank as to -leave uncoated portions which can be secured one to the other by a liquid adhesive and it is not possible to form a wax bond by lheat sealing as on the application of heat, the molten wax is absorbed by the blank. Accordingly, it has been customary when using gloss-waxed blanks either to enclose the goods in a waxed paper bag which'is housed in the carton or to enclose the carton in a waxed paper outer wrapper. The necessity t provide these inner or outer paper wrappings, however, adds to the cost of packing the goods and it is a main object of `the present invention to provide a gloss-waxed carton which can be heat-sealed and which avoids the need for an inner or an outer waxed or other wrapping thereby to reduce the cost of packing.

According t0 the present invention there is provided a carton blank which when set-up to form a carton has portions of one side thereof overlying portions of the opposite side to permit heat-sealing of the overlying portions one to the other, said blank being made of cardboard coated on each of the opposite sides thereof with wax and beneath the wax on said one side with a thermoplastic adhesive composition which is incompatible with the wax, is non-tacky at normal temperatures, and is softened at a temperature higher than the melting temperature of the wax whereby wax disposed between the overlying portions is during the heat-sealing operation melted and absorbed into the overlying portion opposed to that coated with the adhesive composition to provide substantailly wax-free overlying cardboard aneas to be secured one to the other by the adhesive composition located therebetween. In a preferred embodiment of the invention the adhesive composition is coated only on predetermined areas of said one side.

The invention also includes a method of making a carton blank of the kind set out above which includes coating each of the opposite sides of a piece of cardboard with wax and before coating said one side applying thereto, as appropriate, a thermoplastic adhesive composition which is incompatible with the wax, is nontacky at normal temperature, and is softened at a temperature higher than the melting point of the wax, and permitting the adhesive composition to become non-tacky before coating thereof with wax.

The invention also contemplates a method of making a carton from a blank as set forth above, and a carton made from such blank.

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In order that the invention may be clearly understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 illustrates one form of carton blank according to the invention,

FIG. 2 is a section on line II-II, FIG. l, the thickness of the material being exaggerated for the purposes of illustration,

FIG. 3 illustrates a partly set-up carton made from a ,blank as shown in FIG. 1,

FIG. 4 illustrates a carton made from a blank illustrated in FIG. l, and

FIG. 5 illustrates an alternative form of carton blank according to the invention.

Referring to FIGS. 1 to 4 of the drawings, a carton blank is made from cardboard 1, FIG. 2, and the opposite .sides of the cardboard are gloss-waxed by the application to the whole area thereof of coating 2, 3 of a low viscosity paratiin wax. Beneath the wax on one side of the blank, that is beneath the wax coating 3, the cardboard is coated with a thermoplastic adhesive composition 4 which may extend over the whole area of the blank but which, for reasons of economy, is preferably applied only to predetermined areas located adjacent to edge portion of the blank as illustrated in FIG. l, these areas being those which, when the carton blank is set-up to form a carton, are to form the heat seals by which the carton is retained in the set-up condition thereof. The thermoplastic adhesive composition is a composition which is incompatible with the wax, is non-tacky at normal temperatures, and is softened at a temperature higher than the melting temperature of the wax, and the softening temperature of the adhesive composition is preferably appreciably above the melting temperature of the wax, the difference being for example of the order of 20 C. One suitable form of thermoplastic adhesive composition is a polyvinyl acetate resin having incorporated therein plasticizers Which render it theat scalable but non-tacky at normal temperatures when applied to a blank, as illustrated in the drawings.

Blanks made in accordance with the present invention may be, as is customary, formed from a reel of cardboard which is first fed to printing apparatus by which one side of the blank is printed, and thereafter to an adhesive composition applicator of any suitable kind by which the thermoplastic adhesive composition is applied to the side of the cardboard opposite to that on which printing has been effected. The blank is then shaped, in known manner, and provided with score lines or creases about which parts thereof are to be folded and, the adhesive composition having set so as to be non-tacky, the blanks are severed -from the web and suitably stacked for transfer to waxing apparatus of known construction through which the blanks are fed one at a time to be provided on the opposite sides thereof with the coatings 2, 3 of gloss-wax.

The blank shown in FIGURE 1 is constructed to form a carton body portion having a rectangular foursided bottom 5 to the sides of which are hinged a front wall 6, a rear wall 7, and two side walls 8 and 9. In the set-up condition of the body portion the front, rear, and side walls are all retained in the erect condition thereof by infolded corner flaps 10 each of which is folded about a score or crease 11 so that when the corner aps' are folded as illustrated in FIGURE 3, the marginal portions 12 overlie portion 13 of adhesive composition provided on the sides 8 and 9 beneath the gloss-wax coating 3. As indicated in FIGURE 3 by the arrows HP, the marginal portions 12 of the folded corner flaps 10 are heat-sealed to the side walls 8 and 9 by the application thereto of heat and pressure. During the heat-sealing a operation the wax which is disposed between the over. lying portions 12 of the corner flaps 10 and the side Walls 8 and 9 is melted and is absorbed into the marginal portions 12 so as to provide on the sides of the marginal portions which face theside walls 8 and 9 substantially wax-free areas which are secured' by the thermoplastic adhesive composition 13 to the side walls 8 and 9 by the continued application of heat and pressure.

A top 14 is hinged to the rear Wall 7 and, as illustrated in FIGURE 4, is arranged to overlie the bottom 5. The top 14 has hinged thereto a front cover ap 15 and two side lcover liaps 16 and 17. The cover aps 15, 16, 17 are heat-sealed respectively to the outer sides of thel front wall 6 and the side walls 8 and 9 by the application thereto, as indicated by the arrows HP, of heat and pressure, From the drawings it will be seen that the marginal portions of the cover flaps are coated with thermoplastic adhesive compositions these portions being those which are secured to the front and side walls of the carton, and the front cover Hap 15 has a length L whichis substantially equal to the length of the front wall 6. The side cover aps 16 and 17, however, have a length which is slightly less than that of the length of the side walls 8, 9 to which they are heat-sealed, this arrangement being to accommodate a slight bulge 18, FIGURES 3 and 4, which occurs at the corners of the body portion. To ensure a good corner seal at the top corners of the body portion, the side cover flaps are each provided with corner closing portions 19 which extend from opposite free sides of the side cover flaps and respectively to the junction of the front cover ap 15 with the top 14 and to the junction of the rear wall 7 with the top 14.

It will be understood that, as described above with reference to the formation of the body portion of the carton, the closing of the carton after lling thereof is efected by the application of heat and pressure, as in-' dicated in FIGURE 4, so that wax which is located between the front and side walls of the body, and the front and side cover aps is melted and is absorbed into the front and side walls respectively thereby to provide substantially wax-free areas of cardboard which .are secured one to the other by the thermoplastic adhesive composition provided on the cover aps and located between the cover flaps and the front and side Walls.

FIGURE illustrates an alternative form of carton blanks constructed in accordance with the invention as above described, but it will be understood that the invention `can be applied to a carton blank of any desired shape, provided always that the thickness of the cardboard is so selected as to ensure that during the heat-sealing operations the Wax between the overlying cardboard portions to which the heat and pressure is applied will be absorbed into the cardboard in the manner described above thereby to provide substantially wax-free overlying cardboard areas to be secured one to the other by the thermoplastic adhesive composition located therebetween.

We claim:

1. A carton blank which when set-up to form a carton has portions of one side thereof overlying portions of the opposite side to permit heat-sealing of the overlying portions one to the other, said blank being flat and made of cardboard completely coated on each of the opposite sides thereof with wax and beneath the wax on said one side only with a thermoplastic adhesive composition which is incompatible with the wax, is non-tacky at normal temperatures, and is softened at a temperature higher than the melting temperature of the wax whereby wax disposed between the overlying portions is during the heat-sealing operation melted and absorbed into the overlying portion opposed to that coated with the adhesive composition to provide substantially wax-free overlying cardboard areas to be secured one to the other by the adhesive composition located therebetween.

2. A carton blank according to claim 1, wherein the 4 adhesive composition is coated only on predetermined areas of said one side.

3. A carton made of cardboard and comprising a body portion having a rectangular four-sided bottom, a front Wall, a rear Wall, and two side walls all upstanding from the bottom and retained erect by infolded corner flaps, a top hinged to said rear wall and overlyingsaid bottom, and front and side cover flaps depending from the top to overlie the outer sides of the front and side walls respectively, said carton before setting-up thereof being coated all over inside and out with wax, and the front, rear and side walls together with the front and side cover flaps being secured in position by a thermoplastic composition located beneath the wax and exposed by the absorption by the cardboard of wax by the application of heat to the composition coated regions of the carton.

4. A carton according to claim 3, wherein the length of the front cover flap is substantially equal to that of the front wall, the length of the side cover flaps is less than that of the side walls, and the side cover ilaps are each provided with corner closing portions extending from opposite free sides thereof respectively to the junction of the front cover ap with the top and to the junction `of said rear wall with the top.

5. A method of forming a carton having sealed overlapping surfaces comprising the steps of providing a blank for-med ofv fibrous material, applying to one surface only of each of the surfaces to be overlapped a thermoplastic adhesive composition which is incompatible with Wax, then completely coating the blank with wax, next assembling the blank into carton form, and then heating the overlapped surfaces with the wax of the overlapped surfaces being absorbed in the blank and the adhesive composition sealing together the overlapped surfaces.

6. A carton formed from a blank having a thermoplastic adhesive composition on selected areas of one side only and being completely coated with wax, said carton having overlapping sealed areas dened generally by said selected areas, said sealed areas being free of wax and secured together by said thermoplastic adhesive composition, the wax of the sealed areas having been absorbed within the blank material.

7. A method of formi-ng a carton having overlapped sealed surfaces comprising the steps of providing a flat blank formed of fibrous material, applying a thermoplastic adhesive composition which is incompatible with wax to selected areas of said flat blank, then completely coating opposite surfaces of said flat |blank including the `adhesively4 coated areas With Wax, next folding the. blank from its flat state and assembling the blank into carton form with said adhesively coated areas overlying other areas, and then heating the overlapping surfaces with the wax of said overlapped surfaces being absorbed in the blank and the adhesive composition sealing together the overlapped surfaces.

8. The carton blank of claim 1 wherein the application of adhesive composition is limited to a surface to be disposed in opposing relation to another surface in the completed carton and only one of the intended to be opposed surfaces having the adhesive composition thereon.

References Cited by the Examiner UNITED STATES PATENTS 2,341,845 2/ 1944 Mark et al 229-31 X 2,346,488 4/1944 Hoimaster et al. 229-51 X FOREIGN PATENTS 490,316 8/ 1938 Great Britain.

JOSEPH R. LECLAIR, Primary Examiner.

EARLE I. DRUMMOND, Examiner.

D. T. MOORHEAD, Assistant Examiner. 

1. A CARTON BLANK WHICH WHEN SET-UP TO FORM A CARTON HAS PORTIONS OF ONE SIDE THEREOF OVERLYING PORTIONS OF THE OPPOSITE SIDE TO PERMIT HEAT-SEALING OF THE OVERLYING PORTIONS ONE TO THE OTHER, SAID BLANK BEING FLAT AND MADE OF CARDBOARD COMPLETELY COATED ON EACH OF THE OPPOSITE SIDES THEREOF WITH WAX AND BENEATH THE WAX ON SAID ONE SIDE ONLY WITH A THERMOPLASTIC ADHESIVE COMPOSITION WHICH IS INCOMPATIBLE WITH THE WAX, IS NON-TACKY AT NORMAL TEMPERATURES, AND IS SOFTENED AT A TEMPERATURE HIGHER THAN THE MELTING TEMPERATURE OF THE WAX WHEREBY WAX DISPOSED BETWEEN THE OVERLYING PORTIONS IS DURING THE HEAT-SEALING OPERATION MELTED AND ABSORBED INTO THE OVERLYING PORTION OPPOSED TO THAT COATED WITH THE ADHESIVE COMPOSITION TO PROVIDE SUBSTANTIALLY WAX-FREE OVERLYING CARDBOARD AREAS TO BE SECURED ONE TO THE OTHER BY THE ADHESIVE COMPOSITION LOCATED THEREBETWEEN. 